1. Field of the Invention
This invention relates to a plasma address display apparatus which includes a flat panel including a display cell and a plasma cell placed one on the other and peripheral circuits, and more particularly to a plasma address display apparatus which has a high resolution of scanning lines formed on a plasma cell.
2. Description of the Related Art
A plasma address display apparatus is disclosed, for example, in Japanese Patent Laid-Open No. Hei 4-265931 and has such a structure as shown in FIG. 1. Referring to FIG. 1, the plasma address display apparatus shown has a flat panel structure which includes a display cell 1, a plasma cell 2, and a common intermediate sheet 3 interposed between the display cell 1 and the plasma cell 2. The intermediate sheet 3 is formed from a very thin glass plate or the like and called microsheet. The plasma cell 2 is formed from a lower side glass substrate 4 adhered to the intermediate sheet 3, and discharge allowing gas is enclosed in a space defined between the glass substrate 4 and the intermediate sheet 3. Scanning electrodes in the form of stripes are formed on an inner surface of the lower side glass substrate 4.
The scanning electrodes function as anodes A and cathodes K. Barriers 7 are formed such that the anodes A and the cathodes K may be sectioned so that an anode A and a cathode K in pair may be included in each section, and divide the space in which the discharge allowing gas is enclosed to define discharge channels 5 in each of which an anode A and a cathode K are included. Each adjacent ones of the discharge channels 5 are isolated from each other by a barrier 7. The barriers 7 can be formed by printing and baking using screen printing, and contact at the tops thereof with one face of the intermediate sheet 3. Plasma discharge occurs between an anode A and a cathode K in each discharge channel 5 delimited by a pair of barriers 7. The intermediate sheet 3 and the lower side glass substrate 4 are adhered to each other by glass frit or the like.
The display cell 1 includes a transparent upper side glass substrate 8. The glass substrate 8 is adhered to the other face side of the intermediate sheet 3 by a seal member or the like with a predetermined gap left therebetween, and liquid crystal 9 is enclosed as an electro-optical substance in the gap. Signal electrodes Y are formed on an inner surface of the upper side glass substrate 8. Pixels are formed in a matrix at intersecting locations of the signal electrodes Y and the discharge channels 5. Also a color filter 13 is provided on the inner surface of the glass substrate 8, and, for example, three primary colors of R, G and B are allocated to the individual pixels by the color filter 13. The flat panel having such a construction as described above is of the transmission type, and, for example, the plasma cell 2 is positioned on the light incoming side and the display cell 1 is positioned on the light outgoing side of the flat panel. A backlight 12 is mounted on the plasma cell 2 side.
In the plasma address display apparatus having such a construction as described above, the discharge channels 5 in rows are switchably scanned line-sequentially so that plasma discharge may successively occur therein, and image data is applied to the signal electrodes Y on the display cell 1 side in synchronism with the scanning to effect display driving of the plasma address display apparatus. When plasma discharge occurs in a discharge channel 5, then the potential in the discharge channel 5 becomes an anode potential substantially uniformly, and pixel selection for each one scanning line is performed.
In particular, one discharge channel 5 corresponds to one scanning line and functions as a sampling switch. If image data is applied to each pixel in a condition wherein the plasma sampling switch is in a conducting state, then sampling of the image data occurs and lighting or extinction of the pixel is controlled with the sampled image data. After the plasma sampling switch is put into a non-conducting state, the image data is held as it is in the pixel. In other words, the display cell 1 modulates incoming light from the backlight 12 into outgoing light in accordance with image data to display an image based on the image data.
FIG. 2 shows two exemplary pixels of the plasma address display apparatus shown in FIG. 1. Referring to FIG. 2, only two signal electrodes Y1 and Y2, one cathode K1 and one anode A1 are shown in order to facilitate understanding. Each of the pixels 11 has a layered structure including a signal electrode Y1 or Y2, the liquid crystal 9, the intermediate sheet 3 and a discharge channel. The discharge channel is connected to the anode potential almost substantially during plasma discharge. When, in this state, image data is applied to each of the signal electrodes Y1 and Y2, then charge is injected into the liquid crystal 9 and the intermediate sheet 3.
On the other hand, when the plasma discharge comes to an end, then the discharge channel restores an insulating state and comes to have a floating potential, and consequently, the charge injected is held by the pixel 11. In other words, a sampling holding operation is performed. Since the discharge channel functions as an individual sampling switching element provided for each of the pixels 11, it is schematically represented using a switching symbol S1. In the meantime, the liquid crystal 9 and the intermediate sheet 3 held between each of the signal electrodes Y1 and Y2 and the discharge channel function as a sampling capacitor. When the sampling switch S1 is put into a conducting state by line sequential scanning, the image data is written into the sampling capacitor, and a lighting or extinguishing operation of each pixel is performed in response to the data voltage level. Even after the sampling switch SI is put into a non-conducting state, the data voltage is held by the sampling capacitor. An active matrix operation of the display apparatus is performed in this manner. It is to be noted that an effective voltage to be actually applied to the liquid crystal 9 depends upon a capacitance division between the liquid crystal 9 and the intermediate sheet 3.
In the plasma address display apparatus having the structure described above, in order to raise the resolution of an image, the density of pixels arranged in rows and columns must be increased. In order to reduce the size of the pixels in the horizontal direction (direction of a row), the line width of the signal electrodes which extend in the direction of a column should be reduced. On the other hand, in order to reduce the size of pixels in the vertical direction (direction of a column), the arrangement pitch of discharge channels which extend in the direction of a row should be reduced.
However, the discharge channels are isolated from each other by the barriers. From a point of view of a working technique, it is difficult to make the thickness of the barriers extremely thin, and a minimum depth is fixed in order to assure a mechanical strength and so forth. Therefore, if the arrangement pitch of the discharge channels is decreased, then a rate in which the thickness of the barriers occupies increases relatively, and therefore, the area of the aperture of the panel through which light actually passes is sacrificed. In other words, as the number of discharge channels, that is, the number of scanning lines, increases, the numerical aperture of the panel decreases. Further, since the barriers have some height dimension, they intercept rays of light coming in from oblique directions. Accordingly, as the arrangement pitch of the barriers decreases, the rate at which incoming rays of light in oblique directions are intercepted increases and the visual angle when the panel is observed by an observer decreases.
When it is tried to increase the resolution of a plasma address display apparatus, a limitation of a process of production of barriers and scanning electrodes is encountered and a drop of the numerical aperture cannot be avoided. As a result, the brightness of the display unit becomes insufficient. If the amount of light to be emitted from a backlight is increased in order to compensate for the insufficient brightness, then this gives rise to an increase in power consumption. Further, if the barrier and electrode structure is formed further finely, then the ratio at which defects occur increases, and it is difficult to satisfy both of the productivity and the numerical aperture. For example, in the structure of a plasma cell shown in FIG. 3, the discharge channel 5 is formed with an arrangement pitch P of 1,000 xcexcm. The width of the barriers 7 is 200 xcexcm, and the widths of the anode A and the cathode K are 200 xcexcm. Accordingly, the numerical aperture of the panel shown is determined as 1xe2x88x92(200+200+200)/1,000=0.4 and accordingly is 40%. If the arrangement pitch P is decreased from 1,000 xcexcm to 700 xcexcm, then the numerical aperture is determined as 1xe2x88x92(200+200+200)/700=0.14 and thus decreases down to 14%. In this instance, if the electrode widths of the anode A and the cathode K are decreased, then the numerical aperture can be increased to some degree. However, if the electrode widths are decreased, then disconnection and so forth become liable to occur and this gives rise to a drop of the yield. Consequently, the productivity drops remarkably.
It is an object of the present invention to provide a plasma address display apparatus which has a comparatively high numerical aperture and resolution.
In order to attain the object described above, according to an aspect of the present invention, there is provided a plasma address display apparatus, comprising a flat panel wherein a plasma cell having a plurality of scanning electrodes disposed in rows and a display cell having a plurality of signal electrodes disposed in columns are placed one on the other, a scanning circuit for successively applying a selection pulse to the scanning electrodes to effect scanning of the display cell, and a signal circuit for supplying image data to the signal electrodes in synchronism with the scanning by the scanning circuit to write the image data individually for the scanning lines, the plasma cell having a plurality of discharge channels formed in the rows in an isolated relationship from each other such that each of the discharge channels contains discharge allowing gas and has a plurality of scanning electrodes allocated thereto, the scanning circuit successively applying a selection pulse to the plurality of scanning electrodes allocated to each of the discharge channels to cause discharge to occur so that the plurality of scanning lines may be formed in each of the discharge channels.
Preferably, the signal circuit writes image data of the same polarity to the plurality of scanning lines which belong to one discharge channel and writes image data of the opposite polarity into the scanning lines which belong to an adjacent discharge channel to perform ac driving of the display cell.
The plasma address display apparatus may be constructed such that each of the discharge channels includes a pair of barriers which define a space extending in a row, a scanning electrode disposed below each of the barriers, and a central scanning electrode disposed in the middle between the scanning electrodes on the opposite sides in the space, and a scanning line is defined between the scanning electrode disposed below one of the barriers and the central scanning electrode while another one scanning line is defined between the scanning line disposed below the other barrier and the central scanning electrode. In this instance, the scanning circuit may apply a selection pulse to the central scanning electrode to cause discharge to occur in the substantially entire discharge channel and then apply a selection pulse to the scanning electrode disposed below the other barrier to cause discharge to occur in a substantially one half of the discharge channel so that the two scanning lines corresponding to the one half and the other half of the discharge channel may be formed in the discharge channel.
According to another aspect of the present invention, there is provided a plasma address display apparatus, comprising a flat panel wherein a plasma cell having a plurality of scanning electrodes disposed in rows and a display cell having a plurality of signal electrodes disposed in columns are placed one on the other, a scanning circuit for successively applying a selection pulse to the scanning electrodes to effect scanning of the display cell, and a signal circuit for supplying image data to the signal electrodes in synchronism with the scanning by the scanning circuit to write the image data individually for the scanning lines, the plasma cell having a plurality of discharge channels formed in the rows in an isolated relationship from each other such that each of the discharge channels contains discharge allowing gas and has scanning electrodes allocated thereto which function as an anode and a cathode, the scanning circuit successively applying a selection pulse to the scanning electrodes allocated to each of the plurality of discharge channels to cause discharge to occur between the anode and the cathode to form the plurality of scanning lines in the discharge channel making use of a transition state after the discharge, the signal circuit supplying image data to the signal electrodes in response to the transition state after the discharge to write separate image data into the plurality of scanning lines.
Preferably, the signal circuit writes image data of the same polarity to the plurality of scanning lines which belong to one discharge channel and writes image data of the opposite polarity into the plurality of scanning lines which belong to an adjacent discharge channel to perform ac driving of the display cell.
The plasma address display apparatus may be constructed such that each of the discharge channels includes a pair of barriers which define a space extending in a row, and a scanning electrode disposed below each of the barriers and functioning as an anode and a cathode, and a plurality of scanning lines included in each of the discharge channels is spatially separated from each other across the boundary in the middle between the pair of barriers. In this instance, each of the discharge channels may include an additional scanning electrode along the middle between the pair of barriers and assists discharge between the anode and the cathode.
The plasma address display apparatus may be constructed otherwise such that each of the discharge channels includes a pair of barriers which define a space extending in a row and a pair of scanning electrodes disposed between the barriers and functioning as an anode and a cathode, and a plurality of scanning lines included in each of the discharge channels are spatially separated from each other across the boundary in the middle between the pair of barriers.
Each of the plasma address display apparatus according to the present invention described above includes at least two scanning lines formed in each of discharge channels isolated from each other to drive a display cell. In order to form at least two scanning lines in one discharge channel, two scanning electrodes, for example, are provided for one discharge channel. With the plasma address display apparatus, when compared with conventional plasma address display apparatus, the numbers of scanning electrodes and barriers are reduced to one half, and the density of scanning lines is increased at least to twice. Consequently, the resolution of the pixels can be raised as much. From the opposite point of view, where a pixel density may be equal to that of conventional plasma address display apparatus, the arrangement pitch of the display channels can be increased at least to twice. As a result, remarkable augmentation in productivity and numerical aperture can be achieved, and the power consumption of a backlight can be reduced as much. In addition, since the number of barriers decreases to one half, the limitation to the visual angle in the upward and downward directions of a screen is moderated, and also the visual angle can be increased.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.